Power trip: The case for cogeneration

On hot summer days in Sunnyvale, Calif., when power demand soars and peak rates hit their highest levels, Network Appliance Inc.'s 1-megawatt data center drops off the grid. The company's natural-gas-powered cogeneration system delivers all of the power it needs -- and saves it about $300,000 a year in energy costs -- while also providing a source of "free cooling" for the data center.

NetApp's cogeneration system is "reducing energy expense by generating power and cooling when electricity prices are high and gas rates are low," says David Robbins, NetApp's vice president of global infrastructure.

The technology, also known as combined heat and power (CHP), combines a generator with a specialized chiller that turns the exhausted waste heat into a source of chilled water. Technically any power source can be used for CHP, but "natural gas is the most commonly used fuel source for cogeneration in small commercial applications of CHP," such as 5MW, 10MW or 20MW plants serving a single building or campus, says William Kosik, managing principal at EYP Mission Critical Facilities Inc., a New York-based engineering firm that has consulted with NetApp.

In some cases cogeneration facilities use biomass or burn methane from garbage dumps, he says.

Combined Heat and Power

CHP doesn't make sense for every installation, but it should be evaluated during the initial planning stages for any new data center facility, says Peter Gross, CEO of EYP. The evaluation criteria include the following:

•  The price and availability of electricity, taking into account all of the time-of-day tariffs

•  Local climatic conditions

•  Space availability

•  Local permitting requirements and energy regulations

•  The price and availability of natural gas

For its part, NetApp's system includes three natural-gas-powered generators and "adsorption chillers" that can cool the company's 6,000-square-foot data center. The chillers provide cold water through adsorption cooling -- a process that uses a silica-based gel to evaporate water, which serves as the refrigerant. "It has no [chemical] refrigerant. It's very green," says Dan Hoffman, NetApp's director of facilities.

The consistent load profiles of data centers make them well suited to cogeneration, although very few data centers use the technology today, says Peter Gross, CEO of EYP. But the use of cogeneration specifically for data centers is rare: Mark Bramfitt, a principal program manager of customer energy efficiency at Pacific Gas & Electric Co. (PG&E), says he doesn't know of any other data center that uses the technology.

Kosik says there are several reasons to consider cogeneration. For example, having a cogeneration system as an alternative source of power can improve the survivability of a data center during a catastrophic loss of utility power, he says.

"This is a huge concern when we do site evaluations for clients," Kosik says. EYP gathers those numbers in part from information provided by the industry. The number of outages is increasing, he believes, due to an uptick in natural disasters and an aging utility infrastructure. But he doesn't have hard evidence to prove it. "Yes, it's anecdotal," he says.

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